ERROR: expected just one rule action

Can anyone interpret this error message?

It appears in response to each of the following queries in one
instance of PostgreSQL 8.3:
SELECT usecreatedb, usesuper, CASE WHEN usesuper THEN
pg_postmaster_start_time() ELSE NULL END as upsince FROM pg_user
WHERE usename=current_user ;
SELECT rolcreaterole, rolcreatedb FROM pg_roles WHERE rolname =
current_user;
SELECT setting FROM pg_settings WHERE name IN ('autovacuum',
'track_counts');
SELECT oid, *, pg_catalog.shobj_description(oid, 'pg_authid') AS
description FROM pg_roles WHERE NOT rolcanlogin ORDER BY rolname;
SELECT oid, *, pg_catalog.shobj_description(oid, 'pg_authid') AS
description FROM pg_roles WHERE rolcanlogin ORDER BY rolname;

These queries work fine in another instance of 8.3, so it's not the
queries themselves.